There are two basic faceplate panel contours utilized commercially for rectangular cathode-ray tubes having screen sizes greater than about 23 cm diagonal: spherical, and cylindrical. Although flat contours are possible, the added thickness and weight of the faceplate panel required to maintain the same envelope strength are undesirable. Furthermore, if a flat faceplate cathode-ray tube is a shadow mask color picture tube, the additional weight and complexity of an appropriate shadow mask also are undesirable.
Recently, it has been suggested that spherically-shaped cathode-ray tube faceplate panels be improved by increasing the radius of curvature of the panels by a factor of 1.5 to 2. Such increase in radius of curvature reduces the curvature of the faceplate panel, thereby apparently permitting more satisfactory off-axis viewing of a tube screen.
Another new faceplate panel contour concept which creates the illusion of flatness is disclosed in three copending U.S. Applications: Ser. No. 469,772, filed by F. R. Ragland, Jr. on Feb. 25, 1983; Ser. No. 469,774, filed by F. R. Ragland, Jr. on Feb. 25, 1983; and Ser. No. 469,775, filed by R. J. D'Amato et al. on Feb. 25, 1983. The faceplate contour has curvature along both the major and minor axes of the faceplate panel, but is nonspherical. In a preferred embodiment described in these applications, the peripheral border of the tube screen is nearly planar.
When a faceplate panel is made with less curvature, the thickness of the panel must be increased to maintain the structural integrity of the tube envelope. This increase in thickness usually is achieved by adding more wedging to the faceplate panel. Wedging is a center-to-edge thickness increase in a faceplate panel. In prior art tubes, wedging in the order of 1 to 4 mm is present along the diagonals and the major and minor axes of the faceplate panels. Because of this wedging of faceplate panels, the full potential for off-axis viewing through the above-mentioned newer faceplate panels contours cannot be realized.
The present invention provides a novel faceplate panel thickness variation that provides significantly improved off-axis viewing of a cathode-ray tube.